Find your user, and select accounts. Find the subscription you wish to refund and select refund from the frop down box on the right. Note that there is a limited amount of time that a refund can be requested.

Approve:

Go to

Accounting | Payment Refunds

You will see a list of refunds awaiting

Select one.

Change its status to Approved - or not

Hit "Refund Now"

It will process and respond in real time with the result - Approved or Declined - or Error